With the number of users of mobile wireless terminal apparatuses including cellular phones and PHS growing over recent years, the service areas that the base station apparatus covers have become smaller zones. Due to this, the radio waves transmitted from the base station apparatus are likely to arrive at the mobile wireless terminal apparatus only from limited directions. So, the more non-directional, the more effectively an antenna transmits and receives radio waves, regardless of the circumstances.
However, if the operator uses a mobile wireless terminal apparatus close to the human body such as while talking where a practically non-directional antenna is used, the radio waves radiated to the direction of the human body are absorbed into the human body, thereby reducing the radiation efficiency in the human body's direction. Additionally, there have been concerns about the influence of the radio waves absorbed into the human head, in view of which it is preferable that an antenna's directivity is not in the direction of the human body when the mobile wireless terminal apparatus is used at a short distance from the human body.
The invention recited in Japanese Patent Application Publication No. HEI8-288895 concerns a technique for solving the above problems. The invention recited in the above publication is configured such a phase circuit is provided whereby a plurality of antennas are excited given predetermined phase difference, and the radiation of radio waves to the operator and the radio waves absorbed into the human head are reduced, thereby preventing wasteful power consumption while talk is in progress. During the waiting period, there is little need for the reduction of radio waves to the human head, and so causing non-directivity using only one antenna can result in improved antenna efficiency.
Nevertheless, according to the above conventional art, the length of the interval between antenna elements accords with the wavelength, which makes it difficult to apply this conventional technique to mobile wireless terminal apparatuses that have been miniaturized by the remarkable technological developments of late. Another problem is that the amount of a phase shift in a phase shifter is not fixed and needs to be changed depending on the interval between and the position of antenna elements, as a result of which the apparatus becomes complex and the circuit scale increases. Moreover, in recent years, it is not only mobile wireless terminal apparatuses that implement wireless communications, but also such information apparatuses as personal computers and printers implement wireless communications. Still, the above conventional art does not take into account the problem of inefficiency that arises when apparatuses absorb the radiowaves radiated from the above information apparatuses, and the problem of incorrect operation that arises when the apparatuses to which the radio waves are radiated.